FIG. 1 is a block diagram of a network structure of a universal mobile telecommunications system (UMTS) of a 3GPP asynchronous IMT-2000 system. Referring to FIG. 1, a UMTS mainly includes a user equipment (UE), a UMTS terrestrial radio access network (UTRAN), and a core network (CN). The UTRAN includes at least one radio network sub-system (hereinafter abbreviated RNS). The RNS includes one radio network controller (RNC) and at least one base station (Node B) managed by the RNC. At least one or more cells exist in one Node B.
FIG. 2 is an architectural diagram of a radio interface protocol between the UE (user equipment) and the UTRAN (UMTS terrestrial radio access network). Referring to FIG. 2, a radio interface protocol vertically includes a physical layer, a data link layer, and a network layer. Horizontally, the radio interface protocol includes a user plane for data information transfer and a control plane for signaling transfer. The protocol layers in FIG. 2 can be divided into a first layer (L1), a second layer (L2), and a third layer (L3) such as the three lower layers of an open system interconnection (OSI) standard model widely known in the art. The respective layers in FIG. 2 are explained as follows.
A physical layer (PHY) is the first layer and offers an information transfer service to an upper layer using a physical channel. The physical layer (PHY) is connected to a medium access control (MAC) layer located above the physical layer PHY via a transport channel. Data is transferred between the MAC layer and the PHY layer via the transport channel. Moreover, data is transferred between different physical layers, and more particularly, between a physical layer of a transmitting side and a physical layer of a receiving side via the physical channel.
The MAC layer of the second layer offers a service to a radio link control (RLC) layer located above the MAC layer via a logical channel. The RLC layer supports reliable data transfer and is operative in segmentation and concatenation of RLC service data units sent down from an upper layer. Hereinafter, the service data unit will be abbreviated SDU.
A broadcast/multicast control (BMC) layer schedules a cell broadcast message (CB message) delivered from a core network and facilitates broadcasting the message to UEs existing in a specific cell(s). From a UTRAN perspective, the CB message is delivered from a higher layer and is additionally provided with information such as a message ID, a serial number, and a coding scheme, for example. The CB message is delivered to an RLC layer in a BMC message format, and is then delivered to a MAC layer via a logical channel, such as a common traffic channel (CTCH). The logical channel CTCH is mapped to a transport channel, such as a forward access channel (FACH) and a physical channel, such as a secondary common control physical channel (S-CCPCH).
A packet data convergence protocol (PDCP) layer lies above the RLC layer and enables data, which is transferred via a network protocol such as an IPv4 or IPv6, to be efficiently transferred on a radio interface having a relatively small bandwidth. For this, the PDCP layer facilitates reducing unnecessary control information used by a wired network. This function is called header compression, for which a header compression scheme such as RFC2507 or RFC3095 (robust header compression: ROHC), defined by the Internet Engineering Task Force (IETF), can be used. In these schemes, only information mandatory for a header part of data is transferred, thereby reducing data volume to be transferred by transferring a smaller amount of control information.
A radio resource control (RRC) layer is located on a lowest part of the third layer. The RRC layer is defined in the control plane only and is associated with the configuration, reconfiguration and release of radio bearers (RBs) for controlling the logical, transport and physical channels. In this case, the RB is a service offered to the second layer for a data transfer between the UE and the UTRAN. Specifically, the RB is a logical path provided by Layer 1 and Layer 2 of a radio protocol for the data delivery between the UE and the UTRAN The configuration of the RB is a process of regulating characteristics of protocol layers and channels necessary for offering a specific service and a process of setting their specific parameters and operational methods, respectively.
The RRC layer broadcasts system information via a broadcast control channel (BCCH). System information for one cell is broadcast to the UE via a system information block (SIB) format. In case that the system information is changed, the UTRAN transmits BCCH modification information to the UE via a paging channel (PCH) or a forward access channel (FACH) to induce the UE to receive the latest system information.
A multimedia broadcast/multicast service (MBMS) is described below. An MBMS provides a streaming or background service to a plurality of UEs using a downlink dedicated MBMS bearer service. An MBMS includes at least one session. MBMS data is transmitted to a plurality of the UEs via the MBMS bearer service during an ongoing session. The UTRAN provides the MBMS bearer service to UE using a radio bearer (RB). A point-to-point radio bearer is a bi-directional radio bearer and includes a logical channel DTCH (dedicated traffic channel), a transport channel DCH (dedicated channel), and a physical channel DPCH (dedicated physical channel) or a physical channel SCCPCH (secondary common control physical channel). A point-to-multipoint radio bearer is a unidirectional downlink. The point-to-multipoint radio bearer includes a logical channel MTCH (MBMS traffic channel), a transport channel FACH (forward access channel), and a physical channel SCPCH. The logical channel MTCH is configured for each MBMS offered to a cell and is used to transmit user-plane data related to a specific MBMS to a plurality of UEs.
FIG. 3 is a diagram illustrating an example of channel mapping for reception of a point-to-multipoint service by a terminal.
Referring to FIG. 3, a logical channel MCCH (MBMS control channel) is a point-to-multipoint downlink channel and is used in transmitting control information associated with the MBMS. The logical channel MCCH is mapped to the transport channel FACH (forward access channel), while the transport channel FACH is mapped to the physical channel SCCPCH (secondary common control physical channel). At least one MCCH exists within a cell.
The UTRAN that offers the MBMS transmits MCCH information to a plurality of UEs via the MCCH channel. The MCCH information includes a notification message associated with the MBMS (e.g., RRC message associated with the MBMS). For instance, the MCCH information may include a message providing notification of MBMS information, a message providing notification of point-to-multipoint radio bearer information, and/or access information providing notification of an EEC connection being requested for a specific MBMS.
FIG. 4 is a diagram illustrating a protocol stack structure of HS-DSCH in accordance with the related art. HS-DSCH comprises a transmission time interval (hereinafter referred to as “TTI”) of 2 ms length having three slots. A HARQ (Hybrid Automatic Repeat request) scheme is used for HS-DSCH. An AMC (Adaptive Modulation and Coding) scheme is also used for HS-DSCH, whereby the most appropriate combination of a modulation and coding method is selected for the current channel circumstances to achieve optimal throughput.
Referring to FIG. 4, a data unit transferred from an RLC layer of a SRNC is transferred to a MAC-d entity managing transport channels through a logical channel DTCH or DCCH and then is transferred to a MAC-HS entity of a Node B via a MAC-c/sh/m entity of a CRNC. MAC-d, MAC-c/sh/m, and MAC-hs are MAC entities managing transport channels, common channels, and HS-DSCH, respectively.
A physical channel HS-PDSCH is used for delivering a transport channel HS-DSCH. A spreading factor for HS-PDSCH is fixed to 16 and a channelization code is selected for HS-PDSCH among a channelization code set reserved for data transmission on HS-DSCH. When a multi-code transmission is enabled, a plurality of channelization codes are allocated during a sub-frame of HS-PDSCH.
Control information for HS-DSCH is necessary to be transmitted for transmitting user data on HS-DSCH. The control information is exchanged through downlink HS-SCCH (High Speed Shared Control Channel) and uplink HS-DPCCH (High Speed Dedicated Physical Control Channel). HS-SCCH is a downlink physical channel using 16 as a spreading factor and having a data rate of 60 kbps. Information transmitted on HS-SCCH comprises TFRI (Transport Format and Resource related Information), HARQ related information, and an UE identity (H-RNTI) masked to be transmitted for identifying a user to receive the user data. HS-DPCCH is an uplink physical channel through which a UE transmits CQIs (Channel Quality Indicators) for periodically reporting channel status to a Node B and ACK/NACK information for supporting HARQ.
Different scheduling schemes are used during transmitting user data for a service through a downlink shared channel in different cells in the related art. Accordingly, since a UE is unable to receive identical user data through a downlink shared channel from two or more cells at the same time, a diversity gain achieved by combining reception cannot be obtained. Under the foregoing circumstances, when an UE is located at a cell boundary, reception sensitivity for the UE can be deteriorated.